Development of Diphthongs

§ 118. The PG diphthongs (or sequences of monophthongs, see § 56) — [ei, ai, iu, eu, au] — underwent regular independent changes in Early OE; they took place in all phonetic conditions irrespective of environ­ment. The diphthongs with the i-glide were monophthongised into and [a:], respectively; the diphthongs in -u were reflected as long diphthongs [io:], [eo:] and [ea:]. (The changes are shown in Table 2.)

Ifthe sounds in PG were not diphthongs but sequences of two sepa­rate phonemes, the changes should be defined as phonologisation of vowel sequences. This will mean that these changes increased the num­ber of vowel phonemes in the language. Moreover, they introduced new distinctive features into the vowel system by setting up vowels with diphthongal glides; henceforth, monophthongs were opposed to diph­thongs.

Table 2

Old English Reflexes of Proto-Germanic Diphthongs

(or Bi-Phonemic Sequences)

§ 119. All the changes described in § 117, 118 were interconnected. Their independence has been interpreted in different ways.

The changes may have started with the fronting of [a] (that is the change of [a] to [æ]), which caused a similar development in the long vowels; [a:] > [æ:], and could also bring about the fronting of [a] in the biphonemic vowel sequence [a + u], which became [æa:], or more precisely [æ:ə], with the second element weakened. This weakening as well as the monophthongisation of the sequences in [-i] may have been favoured by the heavy stress on the first sound.

According to other explanations the appearance of the long [a:] from the sequence [a+i] may have stimulated the fronting of long

[a:], for this latter change helped to preserve the distinction between two phonemes; cf. OE rād (NE road)and OE r ǣ d (‘advice’) which had not fallen together because while [ail became [a:] in rād, the original

[a:] was narrowed to [æ:] in the word rād. In this case the fronting of [a:] to [æ:] caused a similar development in the set of short vowels;

[a] > [æ], which reinforced the symmetrical pattern of the vowel system.

Another theory connects the transformation of the Early OE vowel system with the rise of nasalised long vowels out of short vowels before nasals and fricative consonants ([a, i, u] plus [m] or [n] plus [x, f, θ or s]), and the subsequent growth of symmetrical oppositions in the sets of long and short vowels (see § 143).